Made to Order (MTO) lenses are produced in very small batch sizes, or as a one-off for a specific patient or a relatively small group of patients. Generally speaking, MTO lenses are lenses for non-standard prescriptions where low demand renders standard commercial batch sizes uneconomic. The very small batch size renders some methods and apparatus of manufacture associated with producing large batch sizes inappropriate. Moreover, as a result of the small batch size several batches of MTO lenses, each batch having different characteristics, will typically be in-process on the same production line at the same time. Maintaining batch integrity therefore becomes a key consideration for MTO lenses.
US Patent Application Publication No. 2010/0109176 discloses the use of machined lens molds in producing MTO lenses. The method disclosed in this application involves forming a plastic ophthalmic lens mold portion blank from a plastic material, and removing a portion of the mold portion blank to form a lens-defining surface having a radius of curvature corresponding to a back surface or a front surface of a lens produced using the lens mold portion. Such machined mold portions may be particularly useful in the manufacture of MTO lenses.
It is desirable to improve the efficiency of the manufacturing process used with MTO mold portions, particularly machined MTO mold portions.